X-57 on stock injectors

X-57 on stock injectors: 365bhp and 300lb ft, and the fuel system never broke a sweat.

The results are in from STealthWerx: 318whp (365bhp on the Dynojet) and 300lb ft of torque from our entry-level X-57 turbo, on the stock fuel pump, stock injectors and a torque cap to look after the gearbox.

Tested the STealthWerx way

Gareth and the guys at STealthWerx are old school in their methods. They do not just buy parts in and sell them on; they spend days and weeks rigorously testing them first, so we knew the X-57 was going to be under the microscope. The new unit was not simply bolted to a car. It was examined, measured and compared with the hugely popular X-47R and with another manufacturer’s unit, and only then, with a twist to the actuator spec, was it fitted.

STealthWerx took their usual due-diligence approach to this new base-model turbo, and both Pumaspeed and the calibration team at MAXD-OUT were fully involved, with one simple goal: find the maximum safe power that can be extracted without over-stressing the stock injectors or fuel system.

The X-57 on the bench before fitting

X-57 kit with dump valve

The complete X-57 kit

Is the X-57 too good for the stock fuel system?

It sounds a simple exercise: turn the boost up from the hugely popular V4702 X-47R mapping, trim the ignition and wastegate duty cycle, and push it to the limit. It is not that simple with a K04-frame turbo this capable. The X-57 has exceptional flow from its new-generation extended-tip seven-blade billet CNC compressor wheel, and when you add a hot side that flows more than an S280 with a unique cut-back turbine wheel, the mapping becomes very involved indeed.

It was quickly found that the stock fuel system on the STealthWerx Fiesta ST200 could not keep up with the new turbo, even on a very low-mileage car. The flow limit of the stock injectors at our self-imposed, super-safe 167 bar was always going to cap the power we could extract.

Built around a safe map

The number one question we get at Pumaspeed is “can my stock engine handle this power?”, so we took the decision to build the first map in the new V57 structure around the stock injector flow limit, dial in sensible boost limits and let the power find its own happy level.

The Fiesta ST has known weaknesses in the gearbox and elsewhere, all of which have to be taken into account, so on almost all MAXD-OUT maps we prefer to keep torque at around 400Nm, or 300lb ft. STealthWerx, MAXD-OUT and the data analysts at Pumaspeed worked slowly through the logs and many iterations of the map until every safety level was dialled in and suitable limits were hard-coded. The result, as always with MAXD-OUT, is a flat torque curve that hangs on and on.

“365bhp is a pretty impressive number for a turbo of this size, but the context is what makes it remarkable”

The numbers in context

• Maximum boost: 1.62 bar (23psi); stock boost is 1.55 bar
• Maximum power: 365bhp at 6,600rpm
• Maximum torque: 300lb ft at 4,000rpm, capped to protect the gearbox
• Air-fuel ratio: 11.5:1 on the stock fuel pump and injectors
• Measured on the Courtney Sport Dynojet, on a 2017 Fiesta ST200 with under 20,000 miles

The X-57 dyno graph: a flat torque curve and boost that holds to the redline

Although K04-frame units are rated to 2.2 bar, these figures were achieved at just 1.62 bar, keeping the stock engine and fuel system happy while managing the extra heat that comes with nearly double the standard power. The graph shows a very stable boost curve: almost fully spooled at 2,500rpm and still making 1.62 bar at 7,500rpm, so there is plenty of headroom and a massive 5,000rpm spread of usable power. The shame is that there is no more fuel flow left in the stock pump and injectors without raising fuel pressure and risking premature wear to the fuel pump tappet and cam.

Day-to-day driveability

Driveability is incredible for a big-turbo car. Gone are the Garrett GTX days of counting the seconds while the turbo spooled at 4,500rpm. The X-57 has achieved its primary goal: lightning-fast performance without compromising real-world usability, and without needing larger injectors or cams. The stock injectors are at their safe limit with this set-up, but a consistent 11.5:1 AFR at full throttle right through the rev range confirms there is still some headroom before the absolute limit.

For people wanting the next level, the X-57R and X-57RS set-ups push past the stock fuelling limits using our uprated Bosch injectors, and we recommend running those only on a built motor to safeguard reliability. The next step for this set-up is simply more fuel: with the larger Bosch injectors and 30% more flow, the X-57 can run a little more boost and ignition and show its true potential.

X57 370bhp turbocharger →X57RS 450 turbocharger →Uprated Bosch injectors →All Fiesta ST180 tuning →

Thanks

Contact Pumaspeed or any of our dealer network to discuss your plans with the X-57 turbo. Our thanks to Gareth Kidman and STealthWerx for once again testing and confirming the capabilities of the X-Series turbos.

All Pumaspeed news & features →